The present invention relates to a forklift truck and to a method of operating a forklift truck.
For example, Japanese Unexamined Patent Application Publication No. 2006-528122 (published Japanese translation of PCT international publication No. WO/2004/103882) discloses a forklift truck for transporting loads. The forklift truck of the Publication has a two-dimensional rangefinder with which to check for the presence of any load on the forks or any obstacle around the forklift truck. The two-dimensional rangefinder emits measurement wave and measures the distance from the emitting source of the measurement wave to a point in an object at which the measurement wave is incident and reflected.
Operation of a forklift truck includes placing or tiering of loads. In the case of placing loads in tiers, the forklift truck places a pallet carrying a second load on the upper surface of a first load, which is placed before the second load. At this time, if the upper surface of the first load is not flat and has a level difference, the second load cannot be placed on the surface. Even if the first load allows the second load to be placed thereon, the second load or the second tier is unstable. Assume that the side of the first load to which the forklift truck approaches is the front of the first load and the side of the first load opposite to the front thereof and away from the forklift is the rear of the first load. If there is a difference in level in the upper surface of the first load and the front part of the upper surface is higher than the rear part, the second load placed on such upper surface tends to tilt rearward. It may be contemplated to detect the level difference in the upper surface of the first load by measuring the distances with the two-dimensional rangefinder. However, if the front part of the upper surface of the first load is higher than the rear part, the measurement wave from the rangefinder is blocked by the front part and does not reach the rear part.